Individual ultrasonic transducers are known, for example, from U.S. Pat. No. 5,603,445. A transducer of that type can be used to secure conductors to semiconductor elements and particularly for making connections between semiconductor elements and substrates. To produce the so-called bond connections, at least one ultrasonic generator produces ultrasound which is coupled into one end of an ultrasonic conductor element at an opposite end of which a tool is provided and which through its vibration, can effect a bonding action or the like.
More particularly, the vibrated tool can effect a cold weld connection between a wire and a substrate or semiconductor chip.
A drawback of this system is that it requires an ultrasound horn between the ultrasonic generator, which can be a piezo element or a stack of piezo elements and produces a vibration practically exclusively in a longitudinal direction.
Ultrasonic transducers provided with horns and cold bonding tools at their ends are fastened in the bonding machine in such manner that the tool carrying end must be free to engage in the longitudinal vibration. The vibration, however, is damped at least in part by the end to press that tool against the part to be bonded.
Since the type of vibration cannot be changed, the tool effectively becomes a monodimensional vibrator, e.g. as described in FIG. 1 of the U.S. Pat. No. 5,603,445 patent so that the wire bonding is effected mainly by frictional movement of the tool. The pressure which must be applied by the tool not only results in a detuning of the entire vibration or oscillation system but it can be detrimental when high precision bonds must be made.
In a publication by Jiromaru Tsujino and Hiroyuki Yoshihara in IEEE International Ultrasonics Symposium, Oct. 5-8, 1998, Metropolitan Hotel, Sendai, Japan, an apparatus for ultrasonic bonding is disclosed in which the two longitudinally oscillating ultrasonic systems are arranged at 90° to one another so that an ultrasonic tool extends perpendicularly to both oscillations systems. It is described that with this system a movement of the tool chip can be effected two-dimensionally in a plane parallel to the substrate and also parallel to the plane in which the ultrasonic generators are arranged. A movement in the height direction with respect to the substrate is not described.